Progressive track width head and method

ABSTRACT

A tape head according to one embodiment includes an array of readers, each of the readers having a track width, wherein the track width of an inner reader of the array is greater than a track width of an outer reader relative thereto. A tape head according to another embodiment includes an array of readers, each of the readers having a track width, wherein the track widths of at least some of the readers progressively decrease in a direction along the array from a middle of the array towards an end of the array.

FIELD OF THE INVENTION

The present invention relates to data storage systems, and moreparticularly, this invention relates to a head having readers of varyingtrack width.

BACKGROUND OF THE INVENTION

Business, science and entertainment applications depend upon computingsystems to process and record data. In these applications, large volumesof data are often stored or transferred to nonvolatile storage media,such as magnetic discs, magnetic tape cartridges, optical diskcartridges, floppy diskettes, or floptical diskettes. Typically,magnetic tape is the most economical, convenient, and secure means ofstoring or archiving data.

Storage technology is continually pushed to increase storage capacityand storage reliability. Improvement in data storage densities inmagnetic storage media, for example, has resulted from improved mediummaterials, improved error correction techniques and decreased areal bitsizes. The data capacity of half-inch magnetic tape, for example, iscurrently measured in hundreds of gigabytes.

The improvement in magnetic medium data storage capacity arises in largepart from improvements in the magnetic head assembly used for readingand writing data on the magnetic storage medium. A major improvement intransducer technology arrived with the magnetoresistive (MR) sensororiginally developed by the IBM® Corporation. Later sensors using theGMR effect were developed. AMR and GMR sensors transduce magnetic fieldchanges to resistance changes, which are processed to provide digitalsignals. AMR and GMR sensors offer signal levels higher than thoseavailable from conventional inductive read heads for a given read sensorwidth and so enable smaller reader widths and thus more tracks per inch,and thus higher data storage density. Moreover, the sensor output signaldepends only on the instantaneous magnetic field intensity in thestorage medium and is independent of the magnetic fieldtime-rate-of-change arising from relative sensor/medium velocity. Inoperation the magnetic storage medium, such as tape or a magnetic disksurface, is passed over the magnetic read/write (R/W) head assembly forreading data therefrom and writing data thereto.

The quantity of data stored on a magnetic tape may be increased byincreasing the number of data tracks across the tape. More tracks aremade possible by reducing feature sizes of the readers and writers, suchas by using thin-film fabrication techniques and MR sensors. However,the feature sizes of readers and writers cannot be arbitrarily reduced.Factors such as lateral tape motion transients and tape lateralexpansion and contraction must be balanced with reader/writer sizes thatprovide acceptable written tracks and readback signals. One particularproblem limiting areal density is misregistration caused by tape lateralexpansion and contraction. Tape width can vary by up to about 0.1% dueto expansion and contraction caused by changes in humidity, tapetension, temperature, etc.

Thus, while the reader/writer array width does not change, the spacingof the data tracks on the tape will vary as the tape expands andcontracts. Ideally, the reader track width would be as wide as the datatrack being read, this would provide the best signal. However, sensortrack widths cannot be made as wide as the data tracks, because thesensors would read adjacent tracks upon expansion or contraction of thetape and/or due to lateral misregistration between tape and head.Accordingly, reader widths are currently designed to be substantiallysmaller than the data track width, and all readers in a given headhaving the same track width. The reader track width is selected toaccommodate the worst case scenarios, i.e., the designer takes intoaccount maximum expansion/contraction and lateral misregistration whendetermining reader track width so that each sensor is over a given trackat any time. FIGS. 1A-1C represent the effect of tape lateral expansionand contraction on reader position relative thereto. FIG. 1A shows thehead 100 relative to the tape 102, where the tape has a nominal width.As shown, the readers 104 are aligned with the data tracks 106 on thetape 102. FIG. 1B shows the effect of tape lateral contraction. Asshown, the outermost readers 108 are positioned along the outer edges ofthe outer data tracks. FIG. 1C shows the effect of tape lateralexpansion. As shown, the outermost readers 108 are positioned along theinner edges of the outer data tracks. Because all of the readers 104have the same width, the readback signal level from each reader willnormally be the same.

One solution to compensate for tape lateral expansion and contraction isto azimuthly rotate the head to a static nominal angle and then makesmall angular adjustments to keep the project reader span aligned withtracks on the tape. This solution is represented in FIGS. 2A-2C. FIG. 2Ashows the head 200 relative to the tape 202, where the tape has anominal width. As shown, the readers 204 are aligned with the datatracks 206 on the tape 202 and the head is rotated by an angle θ_(nom).FIG. 2B shows the head 200 rotated by an angle greater than θ_(nom) tocompensate for tape lateral contraction. FIG. 2C shows the head 200rotated by an angle less than θ_(nom) to compensate for tape lateralexpansion. The problem with this scheme is that the static rotationcauses skew-related misregistration and is generally complex anddifficult to implement. For example rotating heads must be constructedso as not to steer the tape, etc.

SUMMARY OF THE INVENTION

A tape head according to one embodiment includes an array of readers,each of the readers having a track width, wherein the track width of aninner reader of the array is greater than a track width of an outerreader relative thereto.

A tape head according to another embodiment includes an array ofreaders, each of the readers having a track width, wherein the trackwidths of at least some of the readers progressively decrease in adirection along the array from a middle of the array towards an end ofthe array. For example, the track widths of the readers mayprogressively decrease from an innermost reader of the array to anoutermost reader of the array. The track widths may be scaled linearlyfrom the innermost reader to the outermost reader. The track widths mayalso be scaled non-linearly from the innermost reader to the outermostreader. In further embodiments, sets of adjacent readers each have aboutthe same track width, at least three sets of readers being present.

The innermost reader may have a track width at least as wide as awritten data track on a tape adapted for use with the head, butpreferably has a track width that is less than a width of a written datatrack on such a tape. The outermost reader may have any desired trackwidth, and in one embodiment has a track width that is less than about0.6 times a track pitch of a tape adapted for use with the head.

One or more servo readers may be positioned outside the array ofreaders. Writers may also be present on the head.

A tape drive system includes a head as recited above, a drive mechanismfor passing a magnetic recording tape over the head, and a controller incommunication with the head. The head may further include one or moremodules, where the readers are formed on one or more of the modules.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

Prior Art FIGS. 1A-1C illustrate the effect of tape lateral expansionand contraction on a traditional magnetic tape head.

Prior Art FIGS. 2A-2C illustrate rotation of a traditional magnetic tapehead to compensate for the effect of tape lateral expansion andcontraction.

FIG. 3 is a tape bearing surface view of a magnetic tape head accordingto one embodiment of the present invention.

FIG. 4 is a detailed view taken from Circle 4 of FIG. 3 showing thearray of readers according to one embodiment of the present invention.

FIG. 5 is a tape bearing surface view of a magnetic tape head having anarray of readers according to another embodiment of the presentinvention.

FIG. 6 is a tape bearing surface view of a magnetic tape head having anarray of readers according to another embodiment of the presentinvention.

FIG. 7 is a schematic diagram of a tape drive system.

FIG. 8 illustrates a flat-lapped bi-directional, two-module magnetictape head which may be implemented in the context of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is the best mode presently contemplated forcarrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.Further, particular features described herein can be used in combinationwith other described features in each of the various possiblecombinations and permutations.

In the drawings, like and equivalent elements are numbered the samethroughout the various figures.

The present invention includes a multitrack tape head in which thereader track widths are adjusted according to their position in the headso as to maximize track coverage where misregistration is least. Thisinvention may advantageously be implemented using available head andchannel technology and does not require complex mechanisms, etc.

FIGS. 3 and 4 together illustrate a magnetic tape head 300 according toone embodiment of the present invention, where the track widths TW ofthe readers 302 are scaled according to position in the reader array.For illustration, a tape 350 is shown in dashed lines. The tape has databands 0, 1, 2, 3. Servo data 352 is factory-written on the tape 350. InLinear Tape Open (LTO), five servo patterns are written, therebydefining the four data bands 0, 1, 2, 3. Each of the data bands has aplurality of data tracks therein, such as 64 tracks, 128 tracks, etc.Each data band is currently 2.9 mm wide in LTO, but may be any width.Similarly, the servo tracks are approximately 0.19 mm wide, but may belarger or smaller. The illustrative head 300 shown has 16 readers 302,but may have more (e.g., 24, 32, 40) or less. Each reader will typicallyinclude a sensor and shields that surround the sensor. The sensors maybe any type of sensor, including but not limited to GiantMagnetoresistive (GMR) sensors, Anisotropic Magnetoresistive (AMR)sensors, Magnetic Tunnel Junction (MTJ) sensors, etc.

In operation, the servo readers 304 read servo tracks 352 on the tape350. A controller analyzes the servo readback signal and positions thehead 300 at the appropriate position relative to the tape 350 so thatthe readers 302 or writers 360 are over the appropriate data tracks onthe tape 350. If the tape 350 expands, the outermost readers 306 may beadjacent the inside edges of the data tracks, yet the innermost readers308 are aligned with about the center of the middle data tracks. Theservo controller can determine how to center the innermost readers 308on the middle data tracks. Particularly, servo readers 304 have a verysmall track width compared to servo tracks, and the controller candetermine the lateral position of the head 300 relative to the tape 350based on the servo readback signal.

The innermost readers 308 may thus be very close to centrally-alignedwith the inner data tracks, as tape lateral expansion and contractionwill have an increasingly greater effect on the position of the datatracks relative to the outermost readers/writers. Towards the middle ofthe data band, tape lateral expansion should have very little effect ontrack/reader misregistration. Accordingly, the readers 302 can be madewider towards the middle of the array, thereby providing an improvedsignal having greater signal to media noise ratio.

With continued reference to FIGS. 3 and 4, inner readers, preferablyincluding at least the innermost readers 308, have a wider track widththan at least some of the outer readers, i.e., those positioned betweenthe inner readers and the ends of the array, and including the outermostreaders 306, which neighbor servo readers 304 in this embodiment (seeFIG. 3). For example, the track width of the outermost readers 306 maybe set at what it would be in a conventionally designed head, e.g.,about 0.25 to about 0.6 times the track pitch on the tape. The trackwidths of the remaining readers 302 progressively decrease from theinnermost readers 308 to the outermost readers 306. The pitch (center tocenter spacing) between the readers 302 is preferably uniform across thereader array.

The progressively narrowing width of the readers reduces misregistrationdue to mistracking and tape width changes. Tape lateral expansion onsome tapes is approximately 1200 ppm. Thus, for present 16-channel LTOheads, in which the outermost tracks are 2.5 mm apart, the tapeexpansion effect can be as much as 3.0 microns at the outermost readers306, or 1.5 microns per track. This means that the innermost readers 308can be wider by approximately this amount, since these readers 308 canbe precisely positioned over the central data tracks in a given tapewrap, where all 16 heads simultaneously write tracks down the tape. Awider reader provides a lower noise signal. Particularly, making trackwidths of the innermost readers 308 wider can boost SMNR(signal-to-media noise ratio) by an amount proportional to the squareroot of the reader width for the central tracks in future products wherethe written track pitch will approach 2-3 microns. A preferredembodiment has reader track widths scaled linearly from widest at theinnermost readers 308 to narrowest at the outmost reader 306.

An alternate embodiment of the present invention has reader track widthsscaled non-linearly from widest at the innermost readers 308 tonarrowest at the outmost readers 306. FIG. 5 illustrates a head 300where the reader track widths decrease progressively more pronouncedlyfrom the innermost readers 308 to the outmost readers 306. In theembodiment shown, each reader width is smaller than its inner neighborby about 14%. In this example, the progression towards narrower readersis more rapid and thus more conservative.

Yet another embodiment of the present invention, shown in FIG. 6, hasadjacent sets 602, 604, 606, 608, 610 of readers 302 with reader trackwidths being about the same in a given set, where the track widths in agiven set decrease from the innermost set 602 to the outermost sets 606,610. Such an embodiment may be selected for processing considerations.

The track widths of the innermost readers 308 are preferably stillsmaller than the widths of the written data tracks so that tape lateraltransients do not create misregistration. Note that some overlap of thereaders 302 onto adjacent data tracks is permissible, as in anembodiment having filtering and/or implementing a deconvolution scheme.Thus, some reader track widths may be as large as, or larger than, thewritten track widths.

In the heads described above, writers may also be present in a piggybackconfiguration, an interleaved configuration, etc. Any writers presentcan be standard writers, and may all have about the same track width.

FIG. 7 illustrates a simplified tape drive which may be employed in thecontext of the present invention. While one specific implementation of atape drive is shown in FIG. 7, it should be noted that the embodimentsof the previous figures may be implemented in the context of any type oftape drive system.

As shown, a tape supply cartridge 720 and a take-up reel 721 areprovided to support a tape 722. These may form part of a removablecassette and are not necessarily part of the system. Guides 725 guidethe tape 722 across a preferably bidirectional tape head 726, of thetype disclosed herein. Such tape head 726 is in turn coupled to acontroller 728 via a write-read cable 730. The controller 728, in turn,controls head functions such as servo following, writing, reading, etc.An actuator 732 controls position of the head 726 relative to the tape722. The controller 728 may include a processor 734 such as an ASIC,microprocessor, CPU, etc. for performing any of the functions describedherein.

A tape drive, such as that illustrated in FIG. 7, includes drivemotor(s) to drive the tape supply cartridge 720 and the take-up reel 721to move the tape 722 linearly over the head 726. The tape drive alsoincludes a read/write channel to transmit data to the head 726 to berecorded on the tape 722 and to receive data read by the head 726 fromthe tape 722. An interface is also provided for communication betweenthe tape drive and a host (integral or external) to send and receive thedata and for controlling the operation of the tape drive andcommunicating the status of the tape drive to the host, all as will beunderstood by those of skill in the art.

FIG. 8 illustrates a flat-lapped bi-directional, two-module magnetictape head 800 which may be implemented in the context of the presentinvention. As shown, the head includes a pair of bases 802, eachequipped with a module 804. The bases are typically “U-beams” that areadhesively coupled together. Each module 804 includes a substrate 804Aand a closure 804B with readers and writers 806 situated therebetween.In use, a tape 808 is moved over the modules 804 along a tape bearingsurface 809 in the manner shown for reading and writing data on the tape808 using the readers and writers 806.

Standard fabrication techniques can be used to create the readers ofdiffering track widths. For example, the physical width of the sensingportion of the sensor itself may define the track width in someembodiments of the present invention. For instance, when defining theactive widths of the reader sensors during a photolithography process,mask sizes are adjusted to define the desired reader track widths. Inother embodiments of the present invention, the completed ornearly-completed sensor stack can be milled to reduce the physical widthof the sensor. In yet other embodiments of the present invention, theends of the sensor free layers may be pinned via antiparallel couplingwith tab overlays, thereby defining the active track width between thepinned portions of the free layer. In further embodiments of the presentinvention, the ends of the sensor free layers may be pinned viaantiferromagnetic coupling with tab overlays, thereby defining theactive track width between the pinned portions of the free layer. Theseembodiments are presented as only a few examples of the many possibleways that the track width can be defined.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. A tape head, comprising: an array of readers, each of the readershaving a track width, wherein the track width of an inner reader of thearray is greater than a track width of at least some outer readerspositioned on two opposite sides thereof and aligned therewith, whereinthe track widths of the readers progressively decrease from an innermostreader of the array to both outermost readers of the array.
 2. The headas recited in claim 1, wherein the track widths are scaled linearly fromthe innermost reader to the outermost reader.
 3. The head as recited inclaim 1, wherein the track widths are scaled non-linearly from theinnermost reader to the outermost reader.
 4. The head as recited inclaim 1, wherein the inner reader has a track width at least as wide asa written data track on a tape adapted for use with the head.
 5. Thehead as recited in claim 1, wherein the inner reader has a track widththat is less than a width of a written data track on a tape adapted foruse with the head.
 6. The head as recited in claim 1, wherein anoutermost reader has a track width that is less than about 0.6 times atrack pitch of a tape adapted for use with the head.
 7. The head asrecited in claim 1, further comprising an array of writers.
 8. A tapedrive system, comprising: a head as recited in claim 1; a drivemechanism for passing a magnetic recording tape over the head; and acontroller in communication with the head.
 9. A tape head, comprising:an array of readers, each of the readers having a track width, whereinthe track width of an inner reader of the array is greater than a trackwidth of at least some outer readers positioned on two opposite sidesthereof and aligned therewith, wherein three sets of multiple adjacentreaders are present, the readers in a given set having about the sametrack width, wherein readers in at least two nonadjacent sets have aboutthe same track width.
 10. A tape head, comprising: an array of readers,each of the readers having a track width, wherein the track width of aninner reader of the array is greater than a track width of at least someouter readers Positioned on two opposite sides thereof and alignedtherewith; and at least one servo reader positioned outside the array ofreaders.
 11. A tape head, comprising: an array of readers, each of thereaders having a track width, wherein the track widths of at least twoof the readers progressively decrease in a direction along the arrayfrom a middle of the array towards a first end of the array, wherein thetrack widths of at least two other of the readers progressively decreasein a direction along the array from a middle of the array towards asecond end of the array.
 12. The head as recited in claim 11, whereinthe track widths are scaled linearly from an innermost reader to anoutermost reader.
 13. The head as recited in claim 11, wherein the trackwidths are scaled non-linearly from an innermost reader to an outermostreader.
 14. The head as recited in claim 11, wherein an innermost readerof the array has a track width at least as wide as a written data trackon a tape adapted for use with the head.
 15. The head as recited inclaim 11, wherein an innermost reader of the array has a track widththat is less than a width of a written data track on a tape adapted foruse with the head.
 16. The head as recited in claim 11, wherein anoutermost reader of the array has a track width that is less than about0.6 times a track pitch of a tape adapted for use with the head.
 17. Thehead as recited in claim 11, further comprising at least one servoreader positioned outside the array of readers.
 18. The head as recitedin claim 11, further comprising an array of writers.
 19. A tape drivesystem, comprising: a head as recited in claim 11; a drive mechanism forpassing a magnetic recording tape over the head; and a controller incommunication with the head.
 20. A tape head, comprising: a first modulehaving an array of readers and at least one servo reader positionedoutside the array of readers, each of the readers having a track width,wherein the track width of an inner reader of the array is greater thana track width of at least some outer readers positioned on two oppositesides thereof and aligned therewith.
 21. The head as recited in claim20, wherein the track widths of the readers progressively decrease froman innermost reader of the array to an outermost reader of the array.22. The head as recited in claim 20, wherein sets of adjacent readerseach have about the same track width, at least three sets of readersbeing present, no two sets having a common reader.
 23. The head asrecited in claim 20, further comprising a second module opposing thefirst module.
 24. The head as recited in claim 23, wherein the secondmodule also has an array of readers, each of the readers of the secondmodule having a track width, wherein the track width of an inner readerof the array of the second module is greater than a track width of anouter reader relative thereto.
 25. A tape drive system, comprising: ahead having an array of readers and at least one servo reader, each ofthe readers having a track width, wherein the track width of an innerreader of the array is greater than a track width of at least some outerreaders positioned on two opposite sides thereof and aligned therewith;a drive mechanism for passing a magnetic recording tape over the head;and a controller in communication with the head.
 26. The head as recitedin claim 25, wherein the track widths of the readers progressivelydecrease from an innermost reader of the array to an outermost reader ofthe array.
 27. The head as recited in claim 26, wherein the track widthsare scaled linearly from the innermost reader to the outermost reader.28. The head as recited in claim 26, wherein the track widths are scalednon-linearly from the innermost reader to the outermost reader.
 29. Thehead as recited in claim 25, wherein sets of adjacent readers each haveabout the same track width, at least three sets of readers beingpresent.
 30. The head as recited in claim 25, wherein the inner readerhas a track width at least as wide as a written data track on a tapeadapted for use with the head.
 31. The head as recited in claim 25,wherein the inner reader has a track width that is less than a width ofa written data track on a tape adapted for use with the head.
 32. Thehead as recited in claim 25, wherein an outermost reader has a trackwidth that is less than about 0.6 times a track pitch of a tape adaptedfor use with the head.
 33. The head as recited in claim 25, furthercomprising at least one servo reader positioned outside the array ofreaders.
 34. The head as recited in claim 25, further comprising anarray of writers.